Electrowinning is a well-known process for refining a desired metal value. Typically, electrowinning is accomplished in an electrolytic cell containing the desired metal ion in a solution. A cathode and an anode are immersed in the solution. When a current is passed through the electrolytic cell, the desired metal value is plated onto the cathode. The commercial use of electrowinning requires a large number of cathodes and anodes in a single electrolytic cell. Anodes employed in conventional electrowinning operations typically comprise lead or a lead alloy, such as, for example, Pb—Sn—Ca. One significant disadvantage of using such anodes is that during the electrowinning operation small amounts of lead are released from the surface of the anode, and may ultimately cause the generation of undesirable sediments or sludge, particulates suspended in the electrolyte, other corrosion products, or other physical degradation products in the electrochemical cell and/or cause the contamination of the desired metal value.
In addition, in certain copper electrowinning operations, unwanted side reactions on the anode such as deposition and/or accumulation of manganese compounds, such as for example, MnO2 and MnOOH, on the anode may deleteriously impact the copper electrowinning operation.
Attempts to coat an anode to limit the release of undesirable sediments and other physical degradation products or to limit contamination of the desired metal value have been made, but such attempts have yielded an electrolytic cell which demands more power to operate and/or is otherwise undesirable. Exemplary of one prior art coating can be found in U.S. Pat. No. 7,247,229. Improvements are needed for anode coatings, for anodes themselves, and for the electrolytic cell in which anodes are used.